Text Media
When sharing a poem or some other written form of a work with a class, a teacher cannot distribute more than one copy per student. Only two hundred and fifty words can be used from a poem containing two hundred and fifty words or more. Books
As mentioned about "text media" no more than one copy can be distributed per student. When using a children's book only 2 pages can be copied. Books should only be copied if there is no time to ask permission or to obtain enough copies for a class. Books can not be copied more than 9 times during the duration of the class. These rules apply to books, articles, essays, and short stories. Videos
When using videos, the copy of the video on by the teacher must be a legally obtained copy. Videos can only be used for educational purposes in a classroom setting and should not be used solely for entertainment. Viewing the video must be for non-profit reasons. Pictures
When showing pictures to a class, a teacher may show up to five images by the same artist. If the teacher is sharing a collection of photos with their class they may use fifteen photos from that collection, or ten percent. Again the teacher cannot choose whether they show fifteen images or ten percent, it has to be whichever less is. When using pictures that are not already on the internet, permission must be granted before these images can be uploaded to the internet by a student or a teacher.
Text Media
When sharing a poem or some other written form of a work with a class, a teacher cannot distribute more than one copy per student. Only two hundred and fifty words can be used from a poem containing two hundred and fifty words or more.
Books
As mentioned about "text media" no more than one copy can be distributed per student. When using a children's book only 2 pages can be copied. Books should only be copied if there is no time to ask permission or to obtain enough copies for a class. Books can not be copied more than 9 times during the duration of the class. These rules apply to books, articles, essays, and short stories.
Videos
When using videos, the copy of the video on by the teacher must be a legally obtained copy. Videos can only be used for educational purposes in a classroom setting and should not be used solely for entertainment. Viewing the video must be for non-profit reasons.
Pictures
When showing pictures to a class, a teacher may show up to five images by the same artist. If the teacher is sharing a collection of photos with their class they may use fifteen photos from that collection, or ten percent. Again the teacher cannot choose whether they show fifteen images or ten percent, it has to be whichever less is. When using pictures that are not already on the internet, permission must be granted before these images can be uploaded to the internet by a student or a teacher.
More about Fair Use for teachers
http://www.edu-cyberpg.com/Teachers/copyrightlaw.html